CORRESP ONDENCE. 



ic 5 



CORRESPONDENCE. 



NIGHT-AIR IN CITIES. 



To the Editor of the Popular Science Monthly. 



YOUR April correspondent, Mr. C. W. 

 Johnson, in his critique on my brief 

 note which appeared in your pages of Feb- 

 ruary last, either has misapprehended the 

 issue I there made with Dr. Xiemeyer's arti- 

 cle in reference to the salubrity of night as 

 compared with day air in cities, or he has 

 stumbled upon the unwarrantable conclu- 

 sion, solely through the bias of his own cer- 

 ebration, that, because I did not mention, 

 in the short compass of a few lines, all the 

 forms of local urban insalubrity, therefore I 

 do not believe some of them exist. 



Having imagined that I had put the issue 

 so plainly that no reader could foil to under- 

 stand it, I am at a loss to spell it out any 

 clearer for Mr. Johnson. Let me try it in 

 the form of an interrogatory. Is the air in 

 which we live, move, and breathe, more like- 

 ly to be charged from local sources with pol- 

 lutions that produce disease when compara- 

 tively still and calm, as during the night, 

 during the day, when stronger currents are 

 more apt to prevail? Dr. Niemeyer says 

 that the night-air of cities is purer than the 

 day-air, while I, in the language of Mr. 

 Johnson, " assume to correct" his statement 

 by showing by a fact or two that moving air 

 is less apt to be intensely charged by any 

 focus of corruption than that which is al- 

 most motionless and circumjacent to the 

 source of contamination. The issue was 

 made on the point as to the time most fa- 

 vorable for the atmosphere to acquire im- 

 purities the most largely from local sources 

 of pollution, not as to the nature or forms 

 these impurities may assume, or as to wheth- 

 er they are gaseous, granular, molecular, or- 

 ganic, or inorganic. 



Yet, upon the putting of the issue thus 

 plainly, Mr. Johnson represents me as be- 

 lieving that " the insalubrity of city air de- 

 pends upon the amount of non-respirable 

 gases (!) that may be diffused into the re- 

 spirable ones " whatever this may mean 

 " and is wholly independent of the conden- 

 sible effluvia of the vaporous kind, or of the 

 organic germ-dust that the heat and stir of 

 the day may keep suspended." 



In candor I must say that only those 

 whose ideas are crude and vague upon the 

 subject of the atmosphere as a vehicle of 

 contagia or materies morbi would pen such 

 a sentence. Does Mr. Johnson suppose that 

 the contagium vivum of scarlatina, or of ty- 

 phoid fever, or of small-pox, is anything like 



the heavy dust of the streets, or that it 

 needs the stir of day-air to keep it sus- 

 pended ? Does he not know that the con- 

 tagia of these diseases are so subtilely dif- 

 fused and attenuated that the highest mag- 

 nifying power is unable to isolate or detect 

 them ? An investigator now and then has 

 imagined that he has discovered the spores 

 of infection, but only one as yet has made 

 a near approach to settled verification. 



To relieve the mind of Mr. Johnson as 

 to my benighted condition on the subject of 

 germ-dust, I beg to refer him to the Phila- 

 delphia Medical and Surgical Reporter, Jan- 

 uary 13, 1877, in which I take the ground 

 that the theory of a contagium vivum is the 

 only tenable one by which to account for 

 the genesis and spread of some infectious 

 diseases. The unlimited self-multiplication 

 of definite forms or special phases of force, 

 as, e. g.. in small-pox, scarlatina, etc., is an 

 attribute only of living matter. There is 

 no more likelihood of the spores of scarla- 

 tina being converted into those of small-pox 

 than there is of the germ of a dog being 

 converted into that of a horse. All, in com- 

 mon, only reproduce after their kind. 



Of course, the hypothetical spores of an 

 infectious disease are not subject to the 

 chemical law of gaseous diffusion ; yet, as 

 such contagia show in various ways a high 

 degree of volatility, stillness of the air is 

 obviously far more favorable to their large 

 aggregation in any particular locality than 

 rapid air-movement. Every intelligent phy- 

 sician is well aware that one of the very 

 best methods of preventing the spread of 

 an infection through a house is by good 

 ventilation or running air. But all this 

 is against Niemeyer's notion of the superi- 

 or salubrity of still night-air, as compared 

 with the rapid air-movements during the 

 day. The day-air mobility is the analogue 

 of house ventilation the night-air stagna- 

 tion the analogue of concentrated house im- 

 purity. 



If Mr. Johnson desires to know, as it is 

 presumable he does from his inquiry, how 

 " noxious effluvia, if they obey the law of 

 the gaseous diffusion of permanent (!) gases, 

 hover over low marshes and putrefying cess- 

 pools," he has only to study the law in any 

 elementary treatise on chemistry. If the 

 effluvia be sulphuretted hydrocen, it will dif- 

 fuse very rapidly; if it be carbonic acid, 

 much more slowly specific gravity having 

 something to do with the process. But, in 

 either case, the hovering is greatly promoted 

 by the stillness of the atmosphere, as dur- 



